1. Field of the Invention
The present invention relates to a method of forming a substrate made of a Group III-V nitride compound including at least one element from Group IIIB elements and at least nitrogen (N) from Group VB elements.
2. Description of the Related Art
In recent years, demand for high-density recording/reproducing or high resolution in optical disks and magnetic optical disks has grown. To fulfill this demand, researches on semiconductor devices capable of emitting lights in a short-wavelength range such as a green-wavelength spectrum or an ultraviolet spectrum have been actively conducted. Known as suitable materials constituting such a semiconductor device capable of emitting lights in the short-wavelength range are Group III-V nitride compound semiconductors such as GaN, AlGaN mixed crystal or GaInN mixed crystal (Jpn. J. Appl. Phys., 30 (1991), L1998).
In general, light-emitting devices using the Group III-V nitride compound semiconductor are manufactured by sequentially growing layers made of the Group III-V nitride compound semiconductor on a substrate using a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxy (MBE) method. Generally, a sapphire (α-Al2O3) substrate or a silicon carbide (SiC) substrate is used as the substrate.
However, lattice constants and thermal expansion coefficients of sapphire and silicon carbide and those of the Group III-V nitride compound semiconductor are different and thus, there exists a problem such that defects or cracks occur in a grown Group III-V nitride compound semiconductor layer. Further, when manufacturing a laser diode (LD) comprising a semiconductor light-emitting device, it is difficult to form end faces of a resonator by performing cleavage. Therefore, development of a Group III-V nitride compound substrate without such problems has been sought.
However, the Group III-V nitride compound has a high saturated vapor pressure. Thus, a manufacturing method which is generally used when manufacturing a substrate made of silicon (Si) or a substrate made of gallium arsenide (GaAs) cannot be used for the manufacture of the substrate made of the Group III-V nitride compound. Heretofore a well-known method for manufacturing the substrate made of the Group III-V nitride compound is a method such that the Group III-V nitride compound is grown on a growth base made of sapphire or gallium arsenide using a MOGVD method, MBE method or hydride vapor phase deposition method. With the use of the hydride vapor phase deposition method, the Group III-V nitride compound substrate can be grown for several μm to several hundreds μm per one hour, and thus, the Group HI-V nitride compound substrate can be grown to achieve a usable thickness for a short period of time. It has been reported that a GaN substrate is obtained using this method.
However, with the method of growing the Group III-V nitride compound substrate on the growth base, when the Group III-V nitride compound substrate is grown to achieve a usable thickness, cracks occur in the Group III-V nitride compound substrate due to the difference in thermal expansion coefficients of the growth base and the Group III-V nitride compound substrate. Thus, the quality of the substrate is not sufficient, so that a good-quality Group III-V nitride compound semiconductor layer cannot be grown thereon.
Further, disclosed in Japanese Patent Laid-open No. Hei 10-256662 is a method such that a thin GaN substrate with a thickness of about 300 μm is grown over a thick growth base made of sapphire with a thickness of greater than or equal to 1 mm, and then the growth base is removed by means of grinding. With this method, by making the thickness of the growth base larger, warping of the growth base caused by a heat treatment during the growth is suppressed, and deterioration in crystallinity of the GaN substrate caused by the warping of the growth base is prevented. However, with this method, stress increases as the growth base becomes thinner through removal of the growth base, and thus cracks or defects occur in the GaN substrate. Further, since the growth base is thick, over or equal to 1 mm, removal of the growth base is difficult.